HTTP Status Codes Reference — Free
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Remembering whether a condition maps to 409, 422, 423, or 429 is harder than remembering what went wrong. Search the complete response-code list by number or name and browse informational, success, redirect, client-error, and server-error groups.
How it works
- 1
Search a code or phrase
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Review the response category
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Use the canonical reason phrase
About this tool
The five families
Every status belongs to a family that tells you who acts next: 1xx informational, 2xx success, 3xx redirect, 4xx the client must change something, 5xx the server failed. Reading the family first halves debugging time — a 401 and a 403 are different bugs, and neither is a 500.
The codes worth memorizing
200 OK, 201 Created, 204 No Content. 301 permanent move, 302 temporary, 304 not modified. 400 bad input, 401 unauthenticated, 403 forbidden, 404 missing, 409 conflict, 422 unprocessable, 429 rate-limited. 500 internal error, 502 bad gateway, 503 unavailable, 504 gateway timeout. Everything else refines these.
Choosing correctly is an API contract
Clients build behavior on statuses: retry on 503, never on 400; refresh credentials on 401; back off on 429. Returning 200 with an error body breaks that contract — pick the honest code and let the ecosystem work with you.
Frequently asked questions
What is the difference between 401 and 403?
401 means "who are you?" — authenticate and retry. 403 means "I know who you are and you still cannot" — retrying without changing permissions is pointless.
When do I return 400 versus 422?
400 for malformed requests the server cannot parse; 422 for well-formed requests whose content fails validation. The distinction helps clients separate syntax bugs from data bugs.
Why did I get a 502 when the site is up?
A gateway (load balancer, proxy) answered on behalf of the application and the application failed or timed out. The 502 points at the hop between you and the code.